1. Technical Field
The present invention relates to a liquid ejecting head alignment apparatus and a method for alignment thereof. More particularly, the present invention is useful when applied to a high-precision alignment of a liquid ejecting head with an alignment mark printed on a mask made of a transparent material.
2. Related Art
An ink-jet recording apparatus such as an ink-jet printer, a plotter, or the like is provided with ink-jet recording head units. The ink-jet recording head unit has an ink-jet recording head, which discharges ink retained in an ink containing unit such as an ink cartridge, an ink tank, or the like in the form of ink drops. In the following description, such an ink-jet recording head unit may be referred to as “head unit” for simplicity or generalization. The ink-jet recording head has nozzle lines provided in parallel with each other (or one another). Each nozzle line is made of nozzle openings. A cover head is provided to protect the ink-drop-discharge side of the ink-jet recording head. The cover head, which is provided on the ink-drop-discharge surface of the ink-jet recording head, is made up of a window frame portion and sidewall portions. The window frame portion of the cover head has an open window that exposes the nozzle openings. The sidewall portions thereof are formed by bending a cover head material in such a manner that each side thereof extends at a right angle from the window frame portion thereof. Each sidewall portion is bonded to the corresponding side surface of the ink-jet recording head for fixation thereof. An example of such a structure is described and illustrated in, for example, JP-A-2002-160376 (specifically, Page 4, and FIG. 3 thereof).
When bonding a fixation member such as the cover head described above, a holding plate, or the like to a plurality of ink-jet recording heads, each of the ink-jet recording heads is moved with respect to a nozzle plate for positional determination thereof in such a manner that the position of an (each) alignment mark that is provided on the nozzle plate is aligned with a (corresponding) reference mark that is provided on a flat glass mask.
In order to ensure a high precision in such a positional determination, it is necessary to make the distance between the reference mark and the alignment mark as short as possible. As one conventional approach described and illustrated in, for example, JP-A-2004-345281 (specifically, Page 10, and FIG. 3 thereof), alignment is performed with the nozzle plate being in contact with the glass mask.
Disadvantageously, however, if the nozzle plate is in contact with the glass mask, there is a possibility that a foreign object/particle could get jammed between the nozzle plate and the glass mask. In addition thereto, there is a possibility that the surface of the glass mask gets damaged.
Although such a problem will be solved if some space is allocated between the glass mask and the nozzle plate, the existence of a gap therebetween increases a distance between the reference mark and the alignment mark, which adversely affects the precision in positional determination. Specifically, it is necessary to increase the depth of field if a user attempts to observe both the reference mark of the glass mask and the alignment mark of the nozzle plate at the same time by using just a single optical system. However, as the depth of the field becomes greater, it becomes difficult to raise the power of the optical system. This makes it difficult to achieve a high precision in positional determination.
As an alternative approach for observing the reference mark and the alignment mark that are distanced from each other, it is conceivable that, firstly, the reference mark is observed with a focus adjusted on the reference mark, and thereafter, a lens is moved in the optical axial direction so as to observe the alignment mark with a focus adjusted thereon. However, if such a configuration is adopted, since lens move precision directly affects alignment precision, it is difficult to expect positional determination to be carried out with precision higher than a certain level.
It should be noted that the above-identified problems are not unique to alignment performed during production of ink-jet recording head units. That is, the same or similar problems also occur during production of a variety of liquid ejecting head units other than the ink-jet recording head units.